1. Field of the Invention
The present invention relates to a method and apparatus for continuously melting a gelled substance. By utilizing this method and apparatus, substances such as photographic emulsions and other emulsified products that are prepared in the process of manufacturing photographic materials and which have experienced a change from a sol to a gel state as a result of temperature variation can be restored to the initial sol (molten) state.
2. Background of the Invention
In the prior art process of manufacturing photographic materials, photographic emulsions, matting agents and other emulsified products prepared in a sol state are cooled to a gel state and stored at low temperature. In order to coat these emulsified products onto a support, they are restored to their initial sol state by melting the gelled prepared products, as required. Two methods are commonly used to melt such gelled substances. According to one method which is conducted in a batch system, a heat-melting device is placed on the gelled substance in a container and the resulting melt is withdrawn from the container (see, for example, Japanese Patent Publication Nos. 9495/1969 and 1738/1976). In the other method, the gelled substance is continuously fed over a heating surface or into a heating tube, which are moved to promote heat transfer through the gelled substance so that it melts (see, for example, Japanese Patent Publication No. 34816/1974 and Unexamined Published Japanese Patent Application No. 159928/1980).
The method of melting a gelled substance in a batch system has the following problems. Heating of the gelled substance is not uniform and part of it becomes excessively hot while other parts take a long time to completely melt. Also, the amount of gelled substance that can be melted by this method is small and the necessary amount cannot be continuously melted or conveyed when needed. The continuous method has been developed with a view to solving these problems but it still suffers from the following problems. First, the heating area available is limited and if the temperature is increased to an extreme level with a view to achieving a significant increase in the melting speed, the properties of the gelled substance are degraded, the breadth of control of the melting speed is small and the necessary amount of gelled substance cannot be continuously melted or conveyed in accordance with need. Secondly, it takes much time to clean the heating surface. Thirdly, it is impossible to prevent the unmelted substance from flowing out of the container.